TSH

TSH or Thyroid-stimulating hormone (also known as thyrotropin, thyrotropic hormone, TSH, or hTSH for human TSH) is a pituitary hormone that stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3) which stimulates the metabolism of almost every tissue in the body. It is a glycoprotein hormone produced by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid.

Structure

TSH is a glycoprotein and consists of two subunits, the alpha and the beta. The alpha subunit is nearly identical to that of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and human chorionic gonadotropin (hCG). The beta subunit is distinct and confers specificity to the glycoprotein. Each monomeric unit is a glycoprotein molecule; one alpha and one beta subunit make the full, functional TSH.

Function

TSH stimulates the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3). The release of TSH is regulated by an intricate feedback system involving the hypothalamus, the pituitary gland, and the thyroid gland.

Regulation

The levels of TSH are regulated by Thyrotropin-releasing hormone (TRH), which is produced by the hypothalamus, and by the levels of T3 and T4 in the blood. If the levels of T3 and T4 are low, the production of TSH is increased. Conversely, if levels of T3 and T4 are high, then there is a decreased production of TSH.

Clinical significance

TSH tests are used in the diagnosis of certain thyroid disorders, including hypothyroidism and hyperthyroidism. TSH tests are also used to monitor treatment of these conditions and to screen newborns for an underactive thyroid.

See also

• Thyroid function tests
• Hypothyroidism
• Hyperthyroidism
• Thyroid